clocksource: add unregister function to disable unusable clocksources

On x86 the PIT might become an unusable clocksource. Add an unregister
function to provide a possibilty to remove the PIT from the list of
available clock sources.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

3 files changed, 17 insertions, 0 deletions

diff --git a/arch/x86/kernel/i8253.c b/arch/x86/kernel/i8253.c
index 0f8f35458a8f..decc5d294d76 100644
--- a/arch/x86/kernel/i8253.c
+++ b/arch/x86/kernel/i8253.c
@@ -13,6 +13,7 @@
 #include <asm/delay.h>
 #include <asm/i8253.h>
 #include <asm/io.h>
+#include <asm/hpet.h>
 
 DEFINE_SPINLOCK(i8253_lock);
 EXPORT_SYMBOL(i8253_lock);
diff --git a/include/linux/clocksource.h b/include/linux/clocksource.h
index 07b42153de24..85778a4b1209 100644
--- a/include/linux/clocksource.h
+++ b/include/linux/clocksource.h
@@ -215,6 +215,7 @@ static inline void clocksource_calculate_interval(struct clocksource *c,
 
 /* used to install a new clocksource */
 extern int clocksource_register(struct clocksource*);
+extern void clocksource_unregister(struct clocksource*);
 extern struct clocksource* clocksource_get_next(void);
 extern void clocksource_change_rating(struct clocksource *cs, int rating);
 extern void clocksource_resume(void);
diff --git a/kernel/time/clocksource.c b/kernel/time/clocksource.c
index edd5ef8e1765..6e9259a5d501 100644
--- a/kernel/time/clocksource.c
+++ b/kernel/time/clocksource.c
@@ -337,6 +337,21 @@ void clocksource_change_rating(struct clocksource *cs, int rating)
         spin_unlock_irqrestore(&clocksource_lock, flags);
 }
 
+/**
+ * clocksource_unregister - remove a registered clocksource
+ */
+void clocksource_unregister(struct clocksource *cs)
+{
+        unsigned long flags;
+
+        spin_lock_irqsave(&clocksource_lock, flags);
+        list_del(&cs->list);
+        if (clocksource_override == cs)
+                clocksource_override = NULL;
+        next_clocksource = select_clocksource();
+        spin_unlock_irqrestore(&clocksource_lock, flags);
+}
+
 #ifdef CONFIG_SYSFS
 /**
  * sysfs_show_current_clocksources - sysfs interface for current clocksource